Field of the Invention
The present invention relates to a method of controlling deposition of a continuous elongated element in building a tyre for vehicle wheels, to a process and apparatus for building a tyre for vehicle wheels.
Description of the Related Art
A tyre generally comprises a carcass structure including at least one carcass ply having end flaps in engagement with respective annular anchoring structures, each of them being usually made up of at least one substantially circumferential annular insert to which at least one filling insert is applied. A belt structure is associated with the carcass structure, at a radially external position thereof and it comprises one or more belt layers disposed in radially superposed relationship to each other and to the carcass ply and comprising textile or metallic reinforcing cords having a crossed orientation and/or being substantially parallel to the circumferential extension direction of the tyre. Applied at a radially external position to the belt structure is a tread band also of elastomeric material like other semifinished products constituting the tyre. A so-called “under-layer” of elastomeric material can be interposed between the tread band and the belt structure, which under-layer has properties suitable to ensure a steady union of the tread band itself. Respective sidewalls of elastomeric material are further applied onto the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads.
It should be pointed out, to the aims of the present specification that the term “elastomeric material” is understood as indicating a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, this composition further comprises additives such as a cross-linking agent and/or a plasticizer, for example. Due to the presence of the cross-linking agent, this material can be cross-linked through heating, so as to form the final article of manufacture.
It is presently known to make components of elastomeric material of the tyre directly on one or more supports. Note that by “component of elastomeric material” of the tyre in this context it is intended any part of elastomeric material of the tyre (tread band, sidewalls, liner, under-liner, fillers in the bead region, sidewall inserts in run flat tyres, abrasion-proof inserts, for example) or a portion thereof, or yet the assembly formed with two or more of said parts or portions.
Document EP 1 279 486 discloses a method of making a shaped rubber body, such as a green tyre or a component of this tyre, on a rotary support. This rubber body is made through extrusion of a rubber strip by a movable extrusion system, which comprises a screw extrusion unit, a gear pump and an extrusion head provided with an extruder nozzle, connected in series. The rubber strip is fed to a rotary support along a substantially rectilinear passage extending from the screw extrusion unit to the extruder nozzle. The rubber strip is fed to a rotary support along a substantially rectilinear passageway extending from the screw extrusion unit to the extruder nozzle. The rubber strip is further passed through a slit defined between two presser rollers and applied onto an outer surface of the rotary support by one of said two presser rollers.
Document EP 0 968 814 illustrates how to deposit elastomeric material onto a support driven in rotation using a positive-displacement extruder for feeding the elastomeric material, by disposing a pair of rollers rotating in opposite directions in the vicinity of a radially external surface of a supporting portion and using the slit bounded between the rollers as the calender for the elastomeric material coming from the extruder.
Document WO 2008/053278, in the name of the same Applicant, describes an apparatus for building tyres comprising a forming support and an assembling device for assembling components of elastomeric material on the forming support. The assembling device comprises a feeding unit for supplying a continuous elongated element of elastomeric material, a conveyor having a surface movable along a predetermined direction and towards a proximal end thereof adjacent to the forming support; an application device positioned at the proximal end. The continuous elongated element is advanced on the movable surface until the proximal end, and the forming support is rotated to enable application of the continuous elongated element in the form of coils wound up on the forming support. A holding roller is mounted above the movable surface of the conveyor and cooperates with the conveyor for cutting the continuous elongated element at the end of an application step of the latter onto the forming support. The holding roller retains the just cut end of the continuous elongated element supported by the conveyor. The continuous elongated element is therefore ready for a new application on the forming support.
Document WO 2009/040594 in the name of the same Applicant discloses a process for building tyres for vehicle wheels comprising: building a carcass structure on a first forming drum in a carcass-structure building line; building a crown structure on a second forming drum in a crown-structure building line; shaping the carcass structure into a toroid, assembling it to the crown structure in an assembling and shaping station; vulcanising and moulding the green tyre in a vulcanisation and moulding line separated from the carcass and crown building lines.